 /*******************************************************************************
  * Copyright (c) 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.registry;

 /**
  * Aggregated registry timestamp. Corresponds to the current contents of the registry.
  * <p>
  * This class may be instantiated.
  * </p><p>
  * This class is not indended to be subclassed.
  * </p>
  * @since org.eclipse.equinox.registry 3.3
  */
 public final class RegistryTimestamp {
     /**
      * Current aggregated timestamp
      */
     private long aggregateTimestamp;

     private boolean modified;

     /**
      * Public constructor.
      */
     public RegistryTimestamp() {
         reset();
     }

     /**
      * Returns value of the aggregated timestamp.
      * @return value of the aggregated timestamp
      */
     public long getContentsTimestamp() {
         return aggregateTimestamp;
     }

     /**
      * Set value of the aggregated timestamp.
      * @param timestamp the aggregated timestamp of the current registry contents
      */
     public void set(long timestamp) {
         aggregateTimestamp = timestamp;
         modified = false;
     }

     /**
      * Sets aggregated timestamp to the value corresponding to an empty registry.
      */
     public void reset() {
         aggregateTimestamp = 0;
         modified = false;
     }

     /**
      * Determines if the aggregate timestamp was modified using add() or remove()
      * methods.
      * @return true: the timestamp was modified after the last set/reset
      */
     public boolean isModifed() {
         return modified;
     }

     /**
      * Add individual contribution timestamp to the aggregated timestamp.
      * @param timestamp the time stamp of the contribution being added to the registry
      */
     public void add(long timestamp) {
         aggregateTimestamp ^= timestamp;
         modified = true;
     }

     /**
      * Remove individual contribution timestamp from the aggregated timestamp.
      * @param timestamp the time stamp of the contribution being removed from the registry
      */
     public void remove(long timestamp) {
         aggregateTimestamp ^= timestamp;
         modified = true;
     }
 }

